Zeolite synthesis agents

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

Quaternary ammonium compounds as structure directing agents in zeolite synthesis... 

The importance of quats as structure-directing agents in zeolite synthesis was recently underlined (ref. 5) by the synthesis of the new zeolites SSZ-26 and -33, which combine 10- and 12-ring pores. The templates applied are shown in Figure 3. 

Since then, organic amines, quaternary-ammonium bases, metal complexes, and other compounds have been extensively used in zeolite synthesis, acting as space fillers with low specificity, structure-directing agent, or true templates ... 

Zeolite synthesis around a metal complex was introduced by Balkus [40]. The metal complex is added to the zeolite synthesis mixture and is incorporated into the zeolite structure during the zeolite synthesis. Of course, this procedure is only applicable when the metal complex is soluble in the synthesis mixture and can withstand the hydrothermal synthesis conditions. Another requirement is that the zeolite structure-directing agent added must be removable by a milder... 

New methods are focused on the preparation of solid catalysts without release of gaseous or liquid waste streams. In zeolite synthesis, the chemical compounds generated during combustion of templates (structure-directing agent) are often hazardous and harmful to the environment. A new method teaches disassembling the template within zeolite pore space into small fragments without combustion. ... 

Nuetral templates may not be bound to the zeolite surface but simply trapped. This is the basis of our zeolite synthesis method for the preparation of ship-in-a-bottle metal complexes, ie crystallization of the zeolite around a metal chelate complex. Zeolite encapsulated metal complexes have many applications, ranging from shape selective catalysis [9] to magnetic resonance imaging contrast agents [10]. 

Zeolites are prepared hydrothermal synthesis. A simplified scheme of the zeolites synthesis is depicted in Figure 11.6 The basic ingredients -SiO, Na SiOj or Si(OR) and Al O, NaAlO, or Al(OR)j - together with a structure directing agent (template), usually an amine or surfactant like tetra-alkyl ammonium salt, are added to aqueous alkali (pH 8-12) which results in the sol-gel consisting monomeric and oligomeric silicate species. 

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